A state-of-the-art arrangement for dispensing predetermined dosage quantities of substances can include for example an electronic laboratory balance, a dosage-dispensing instrument with a reservoir container and a metering head, as well as an electronic control instrument, for example a microcomputer. The dosage-dispensing instrument is arranged so that the outlet opening of the metering head is located above the weighing pan. The reservoir container is filled with the dosage material, and a weighing container is placed on the weighing pan in centered vertical alignment below the outlet opening of the metering head. The balance, the control instrument and the dosage-dispensing instrument constitute a closed-loop control system in which the control instrument continuously receives the actual weight of the substance that is currently present in the weighing container, compares the weight signal to a preset target weight and, based on the difference between the actual weight and the target weight, issues a control signal to the metering head. This control system allows the outflow of substance from the dosage-dispensing instrument into the weighing container to be controlled, for example in such a way that the flow of substance is slowed down as the actual weight approaches the target weight and is stopped when the target weight is attained, wherein the amount of substance that is in free fall at any time of the process can be taken into account through a lead time allowance.
In serial weighing-in processes of multiple samples or in gravimetric dosage-dispensing processes with the state-of-the-art arrangement of the foregoing description, the weighing containers are set individually on the weighing pan, aligned with the outlet opening of the dosage-dispensing device, and removed from the weighing pan after the dispensing process has been completed. If this process is performed by hand, it is not only very labor-intensive but also involves the risk that substance is spilled or that weighing containers get mixed up. Alternatively, the transfer of the weighing containers to and from the weighing pan can also be automated, for example with a so-called auto-sampler or a laboratory robot. However, the expense for such arrangements can only be justified for very high-volume dosage-dispensing applications.
It is therefore an objective to provide a suitable accessory device for a balance which allows serial weighing-in processes of multiple samples or gravimetric dosage-dispensing processes to be carried out more efficiently and without involving major technical measures, so that the weighing containers can be brought one after another precisely into a defined position, for example below the outlet opening of a dosage-dispensing device, in a quick and easy way and in particular with only a small amount of manual handling.